Let’s take an example. What’s the difference between “I will never forget to lock the door” and “I will never forget locking the door”? Well, “I will never forget to lock the door” is a promose to lock the door in the future.

 

 You are saying that every time you leave your home in the future, you will remember to lock the door. On the other hand, “I will never forget locking the door” means that you locked the door one time in the past.

 

And that for some reason, the memory of locking the door that time will never be forgotten. Maybe you locked yourself into your house and couldn’t get out for a week.

So, if you are reminding someone to do something in the future, say, “Don’t forget to bring your keys.” “Don’t forget to come early tomorrow.” Or “Don’t forget to turn off the TV.”

 

On the other hand, if you are telling someome about a memory of doing something in the past that you will always remember, you say, “I will never forget seeing the Statue of Liberty for the first time” or “I will never forget getting lost in Tokyo.”

 

 “forget doing something” is always used in the negative “I can’t forget” “I won’t forget” “I will never forget”. So the meaning is the same as remember doing something.
Pay special care when using the word “forget”.

 

You must choose the right form of the verb you use after it.